(a) The date of December 31, 1974, shall be the base date in determining the reporting year according to the number of members in a pension system.
(b) The reporting year for municipalities which have less than 50 members in each of its pension systems shall be once every 4 years beginning from the base date.
(c) The reporting year for municipalities which have 50 or more members in any of its pension systems shall be once every 2 years beginning from the base date.